1. Field of the Invention
The invention relates to the field of electronic packaging and assembly of electrical components, and more particularly, the invention relates to a system and method for preventing moisture damage to electrical components by maintaining a dry atmosphere in the storage area of a component placement machine.
2. Brief Description of the Related Art
Plastic cases for electronic active components or integrated circuits are gaining in popularity over ceramic or metallic packages as they are easier to work with and less expensive. They have, however, the disadvantage of being sensitive to moisture. Moisture from atmospheric humidity is absorbed by the package via permeation. If the moisture level inside the package reaches a critical point, the device may be damaged when brought up to temperature during the reflow soldering process. These types of moisture induced failures are referred to as the popcorning effect due to the audible popping when a crack appears in the package from moisture overpressure. If cracking occurs, air and moisture may contact the silicon die inside the package resulting in corrosion. The reliability of the product is seriously jeopardized if an integrated circuit package cracks during reflow. Micro-cracking is also hard to detect. Therefore, it is critical for printed circuit board assemblers to avoid moisture induced failures and popcorning defects and to limit the exposure of components to moisture.
There are currently no specific solutions to prevent the absorption of moisture. Assemblers normally adopt a “moisture management system” in order to control the moisture exposure levels. A part of such a system involves re-bagging the components in dry and desiccant bags after an initial usage. Another part of the current practice is to monitor floor life of a component or the time that the component is exposed to atmosphere moisture. After a floor life has expired, the moisture in the package may be reduced by performing a process referred to as “baking” during which the component is heated to remove moisture.
The limit level or critical moisture level (level at which cracking will occur) for a package depends on the package itself and the temperature at which it will be exposed during the assembly/soldering process. A higher reflow temperature results in a lower critical moisture level. The determination of the weight gain percent failure level is therefore component specific and process specific.
While baking prevents the moisture-induced failure and the popcorning effect, it is time consuming and may be difficult to manage. For example, products qualifying with a moisture sensitivity corresponding to the IPC/JEDEC J-STD-020 standard are normally baked at an elevated temperature for a period varying from 24 hours (baked at 125° C.) to a week or more (baked at 40° C.). Sometimes this baking process is shortened or interrupted by the assembler because the components are urgently required to finish a production load that is back ordered. Baking also oxidizes the components and ages them by growing the intermetallic layer of the component joint structure.
As the reflow soldering temperatures are expected to increase when lead-free alloys are introduced on the market (217° C. and higher melting points for lead-free alloys versus a 183° C. melting point for standard lead alloys) moisture control will become even more critical in the future.
Accordingly, it would be desirable to provide a system which eliminates the need for baking and still prevents moisture absorption and the associated moisture induced failure, including popcorning.
It would also be desirable to provide a system to remove moisture from components without baking.